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Ni-Mn-Ga-Fe 강자성 형상기억합금의 미세파괴기구 및 파괴성질
어광준 ( Kwang Jun Euh ),이정무 ( Jung Moo Lee ),남덕현 ( Duk Hyun Nam ),이성학 ( Sung Hak Lee ) 대한금속·재료학회 2009 대한금속·재료학회지 Vol.47 No.12
The fracture toughness improvement of Ni-Mn-Ga-Fe ferromagnetic shape memory alloys containing ductile particles was explained by direct observation of microfracture processes using an in situ loading stage installed inside a scanning electron microscope (SEM) chamber. The Ni-Mn-Ga-Fe alloys contained a considerable amount of ductile particles in the grains after the homogenization treatment at 800~1100℃. γ particles were coarsened and distributed homogeneously along β grain boundaries as well as inside β grains as the homogenization temperature increased. The in situ microfracture observation results indicated that γ particles effectively acted as blocking sites of crack propagation, and provided stable crack growth that could be confirmed by the R-curve analysis. This increase in fracture resistance with increasing crack length improved overall fracture properties of the alloys containing γ particles.
고에너지 전자빔 투사방법으로 제조된 VC/탄소강 표면합금화 재료의 미세조직 형성과 물성 향상
魚光俊,李聖鶴 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.4
The present study is concerned with the microstructural evolution and property improvement of VC/ carbon steel surface-alloyed materials fabricated by high-energy electron-beam irradiation. The mixtures of VC powders and flux (50%MgO-50%CaO or CaF_2) were placed on a plain carbon steel substrate, and then electron beam was irradiated on these mixtures using an electron beam accelerator. The surface-alloyed layers of 1.2∼3 ㎜ in thickness were homogeneously formed without defects, and contained a large amount (up to 10 vol.%) of VC precipitates in the bainitic or martensitic matrix. This microstructural modification including the formation of hard precipitates and hardened matrix in the surface-alloyed layers improved hardness and wear resistance. Particularly in the surface-alloyed material fabricated with the lower input energy density, the wear resistance was greatly enhanced over the steel substrate because of the increased size and volume fraction of VC particles, although the thickness of the surface-alloyed layer decreased. Microstructural modifications including melting, solidification, precipitation, and phase transformation processes of the surface-alloyed layer could also be explained from a thermal transfer modeling and a Fe-V-C ternary phase diagram.
고에너지 전자빔 투사방법에 의한 붕화불/Ti-6Al-4V 표면합금재료의 제조와 미세조직분석
이종민,어광준,이성학 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.6
The present study is concerned with fabrication and microstructural analysis of boride/Ti-6Al-4V surface-alloyed materials using irradiation of high-energy electron beam. Mixtures of TiB₂ or MoB boride powders and CaF₂ flux were placed on a Ti-6AI-4V alloy substrate, and then electron beam was irradiated on these mixtures using an electron beam accelerator. In the specimens processed with a flux mixing ratio of 40 wt.%, the melted region of 1.1∼1.5 ㎜ in thickness was homogeneously formed without defects, and contained a large amount of TiB borides. This microstructural modification including the formation of TiB borides and β-Ti matrix in the surface-alloyed layers greatly improved hardness, about twice higher than hardness of the Ti alloy substrate. These findings suggested that the surface-alloying using high-energy electron beam irradiation was economical and useful for the development of titanium-base surface-alloyed materials with improved hardness.
고에너지 전자빔투사방법에 의해 제조된 TiB2 표면합금화 재료의 미세조직 연구
신기삼,어광준,이성학 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.5
The present study is concerned with the processing and the microstructural analysis of surface alloyed materials with TiB₂ powders using irradiation of high-energy electron beam. The mixtures of TiB₂ powders and flux were deposited on a plain carbon steel plate, and then electron beam was irradiated on these mixtures using an electron beam accelerator. The microstructures of the irradiated surface layers were examined by optical and scanning electron microscopy. A few residual micropores were found in the sample processed without flux, but their number was decreased in the samples processed with a considerable amount of flux. As a result of irradiation, the Ti content was homogeneously maintained throughout the melted region, whose hardness was greatly improved. This was associated mainly with the microstructural modification including the segregation of Ti and B along solidification cell boundaries and the formation of fine Ti(C,M) particles.
Joon‑Young Heo,Min‑Seok Baek,Kwang‑Jun Euh,Kee‑Ahn Lee 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.5
This study investigated the microstructure, tensile and fatigue properties of Al–5 wt.%Mg alloy manufactured by twin rollstrip casting. Strips cast as a fabricated (F) specimen and a specimen heat treated (O) at 400 °C/5 h were produced andcompared. In the F specimen, microstructural observation discovered clustered precipitates in the center area, while in theO specimen precipitates were relatively more evenly distributed. Al, Al 6 (Mn, Fe), Mg 2 Al 3 and Mg 2 Si phases were observed. However, most of the Mg 2 Al 3 phase in the heat-treated O specimen was dissolved. A room temperature tensile test measuredyield strength of 177.7 MPa, ultimate tensile strength of 286.1 MPa and elongation of 11.1% in the F specimen and167.7 MPa (YS), 301.5 MPa (UTS) and 24.6% (EL) in the O specimen. A high cycle fatigue test measured a fatigue limit of145 MPa in the F specimen and 165 MPa in the O specimen, and the O specimen achieved greater fatigue properties in allfatigue stress conditions. The tensile and fatigue fracture surfaces of the above-mentioned specimens were observed, and thisstudy attempted to investigate the tensile and fatigue deformation behavior of strip cast Al–5 wt.%Mg based on the fi ndings.
고에너지 전자빔 투사방법으로 제조된 VC / 탄소강 표면합금화 재료의 템퍼링에 의한 경도향상
이성학(Sung Hak Lee),어광준(Kwang Jun Euh),김용찬(Yong Chan Kim),신기삼(Kee Sam Shin),김락준(Nack J. Kim) 대한금속재료학회 ( 구 대한금속학회 ) 2002 대한금속·재료학회지 Vol.40 No.9
This study aimed at improving hardness by tempering of VC/carbon steel surface-alloyed material fabricated by high-energy electron-beam irradiation. The mixture of VC powders and flux (50%MgO-50%CaO) was placed on a plain carbon steel substrate, and then electron beam was irradiated on this mixture using an electron beam accelerator. The surface-alloyed layer of 1.8 mm in thickness was homogeneously formed without defects. The microstructural analysis indicated that VC particles were coarsely formed along solidification cell boundaries, and the matrix inside cells was mostly composed of lath-type martensite and fine cuboidal VC particles. A large amount (10.1 vol.%) of these VC particles in the lath-type martensitic matrix improved hardness four times greater than that of the substrate. When the VC/steel surface alloyed material was tempered, a number of fine VC particles were precipitated in, the tempered martensitic matrix, thereby leading to the additional hardness improvement. Therefore, the hardness of the surface-alloyed layer was further enhanced by tempering, while the residual stress in the layer could be removed and the fracture toughness could be increased.
고에너지 전자빔투사방법을 사용한 TiB2/Ti 표면합금화 재료의 제조 연구
구양모,이성학,어광준,김낙준,오준철 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.12
The present study is concerned with the fabrication and the microstructural analysis of a TiB₂/Ti surfacealloyed material fabricated by high-energy electron beam irradiation. The mixture of TiB₂ powders and flux was deposited on a Ti-10V-2Fe-3Al alloy substrate, and then electron beam was irradiated on these mixture using an electron beam accelerator. The melted region of about 1.5 ㎜ thickness was homogeneously formed without pores or cracks, and was composed of primary and eutectic TiB borides in the β phase matrix. The formation of these TiB borides greatly improved hardness, especially high-temperature hardness up to 450℃. These findings suggested that the surface-alloying method using high-energy electron beam irradiation was economical and useful to the development of new advanced materials with improved high-temperature properties.